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Sunday, August 4, 2013

A Defense of Computational Physics

This is a defense a long time in the making (h/t Dan Hughes). Patrick Roache has done short articles along a similar vein defending the Computational Physics enterprise against what amounts to an empty nihilism that seems to be popular among academics.

Here is the publisher's description,Karl Popper is often considered the most influential philosopher of science of the first half (at least) of the 20th century. His assertion that true science theories are characterized by falsifiability has been used to discriminate between science and pseudo-science, and his assertion that science theories cannot be verified but only falsified have been used to categorically and pre-emptively reject claims of realistic Validation of computational physics models. Both of these assertions are challenged, as well as the applicability of the second assertion to modern computational physics models such as climate models, even if it were considered to be correct for scientific theories. Patrick J. Roache has been active in the broad area of computational physics for over four decades. He wrote the first textbooks in Computational Fluid Dynamics and in Verification and Validation in Computational Science and Engineering, and has been a pioneer in the V&V area since 1985. He is well qualified to confront the mis-application of Popper's philosophy to computational physics from the vantage of one actively engaged and thoroughly familiar with both the genuine problems and normative practice.
Here is a short excerpt from one of Roache's papers that gives a flavor of the argument he is addressing,

In a widely quoted paper that has been recently described as brilliant in an otherwise excellent Scientific American article (Horgan 1995), Oreskes et al (1994) think that we can find the real meaning of a technical term by inquiring about its common meaning. They make much of supposed intrinsic meaning in the words verify and validate and, as in a Greek morality play, agonize over truth. They come to the remarkable conclusion that it is impossible to verify or validate a numerical model of a natural system. Now most of their concern is with groundwater flow codes, and indeed, in geophysics problems, validation is very difficult. But they extend this to all physical sciences. They clearly have no intuitive concept of error tolerance, or of range of applicability, or of common sense. My impression is that they, like most lay readers, actually think Newton’s law of gravity was proven wrong by Einstein, rather than that Einstein defined the limits of applicability of Newton. But Oreskes et al (1994) go much further, quoting with approval (in their footnote 36) various modern philosophers who question not only whether we can prove any hypothesis true, but also “whether we can in fact prove a hypothesis false.” They are talking about physical laws—not just codes but any physical law. Specifically, we can neither validate nor invalidate Newton’s Law of Gravity. (What shall we do? No hazardous waste disposals, no bridges, no airplanes, no...) See also Konikow & Bredehoeft (1992) and a rebuttal discussion by Leijnse & Hassanizadeh (1994). Clearly, we are not interested in such worthless semantics and effete philosophizing, but in practical definitions, applied in the context of engineering and science accuracy.Quantification of Uncertainty in Computational Fluid Dynamics, Annu. Rev. Fluid. Mech. 1997. 29:123–60